This invention relates to ultrasonic apparatus, and especially to ultrasonic surgical apparatus and methods for ultrasonic surgical fragmentation and removal of tissue. More particularly, this invention relates to a method and apparatus for pulsing or modulating the vibration of an ultrasonically vibrating tip to control its duty cycle for improving its cutting characteristics. Still more particularly, this invention relates to a method and apparatus for continuously controlling the duty cycle of an ultrasonic device, in discrete preset increments, between predetermined high and low amplitudes in variable programmed groups, or continuously in response to a remotely sensed parameter for accurately controlling ultrasonic energy delivered to the operating fluid.
Devices which effectively utilize ultrasonic energy for a variety of applications are well-known in a number of diverse arts. The application of ultrasonically vibrating surgical devices used to fragment and remove unwanted tissue with significant precision and safety has thus led to the development of a number of valuable surgical procedures. Accordingly, the use of ultrasonic aspirators for the fragmentation and surgical removal of tissue from a body has become well-known. Initially, the technique of surgical aspiration was applied for the fragmentation and removal of cataract tissue as shown, for example, in U.S. Pat. Nos. 3,589,363 and 3,693,613. Later, such techniques were applied with significant success to neurosurgery and other surgical specialties where the application of ultrasonic technology through a small, hand-held device for selectively removing tissue on a layer-by-layer basis with precise control has proven feasible.
Certain devices known in the art characteristically produce continuous vibrations having a substantially constant amplitude at a frequency of about 20 to 30 kHz up to about 40 to 50 kHz. U.S. Pat. No. 3,589,363 describes one such device which is especially adapted for use in the removal of cataracts, while U.S. Pat. No. 4,063,557 describes a device suitable for the removal of soft tissue which is particularly adapted for removing highly compliant elastic tissue mixed with blood. Such devices are continuously operative when a surgeon wishes to fragment and remove tissue, and generally operate under the control of a foot switch.
Certain limitations have emerged in attempts to use such devices in a broad spectrum of surgical procedures. For example, the action of continuously vibrating device did not have a desired effect in breaking up certain types of body tissue, bone, or concretations. Because the range of ultrasonic frequency is limited by the physical characteristics of a hand-held device, only the motion available at the tip was a focal point for improving the cutting characteristics of the instrument. This limited focus proved to be ineffective for certain applications because either the motion available at the tip was insufficient to fragment and remove hard tissue at a surgically-acceptable rate, or the available stroke and stroke amplitude was so large as to cause excessive damage to surrounding tissue and the vaporization of fluids at the surgical site so as to obscure the view of the surgeon. Accordingly, there has been a need in the art for a method and ultrasonic apparatus in which the cutting range and efficiency of the vibrating device can be extended for safe and efficacious tissue removal.
Thus, it is another overall objective to provide a method and ultrasonic apparatus for accurately controlling energy as it is transmitted to tissue so as to enhance its cutting action in both hard nd soft tissue, while maintaining the temperature in the surrounding tissue below a preset level. In this context it is desirable to utilize a higher stroke level than can otherwise be surgically tolerated without exceeding the allowable average energy, i.e., to simulate the effect of a high stroke level with a lower stroke level. It is also an objective to improve the visibility and control of the cutting action when fragmenting soft tissue and to utilize higher stroke levels for improved but safe fragmentation without damage to surrounding tissue areas as is characteristic of prior art devices.
In addition, since it is known that precisely controlled heating of certain types of cancerous and tumorous tissue may have a beneficial effect, it is another overall objective of this invention to provide a method and apparatus for precisely raising the temperature in tissues surrounding the tumorous growth to a preset level.
It is apparent that prior art concepts did not suggest such an invention. For example, U.S. Pat. No. 3,812,858 describes a dental electrosurgical device known to the art which regulates the application of RF power through an active electrode to a patient according to the resistance of the tissue, and further incorporates a duty cycle timer to regulate the period of active current flow and interrupt repeatedly active current flow to the patient. However, such relatively lengthy periods of interruption are not practicable in an ultrasonic unit which can cause the surgeon to have to wait for a reapplication of power, perhaps at crucial points in the surgery, and such techniques have not been applied to ultrasonic surgical apparatus of the type with which this invention is concerned.
In an ultrasonic machining method and apparatus, as discussed in U.S. Pat. No. 4,343,111, the vibratory oscillations applied to the machining tool are periodically interrupted so that the oscillations are applied in the form of a series of time-spaced bursts, for ultrasonically machining irregular contours. Such a device does not suggest its applicability to ultrasonic surgery or instrumentation and the technique there discussed is hardly directed to the problem solved by this invention.
The objects described above and other purposes of this invention will become apparent from a review of the written description of the invention which follows, taken in conjunction with the accompanying drawings.